A base cloth for reinforcement is sometimes used for composite molded products such as FRP (fiber-reinforced plastic), cement, concrete, tarpaulin, etc. For example, for tennis rackets, fishing rods, etc., base cloths made of a high-strength, and high-modulus multifilament of carbon fiber, glass fiber, aromatic polyamide fiber or the like are used in a form bound with matrix resins such as epoxy resins, etc. Also, for the reinforcement of cement and concrete, alkaline-resist vinylon fibers, etc. are sometimes used as a reinforcing base cloth. Further, for the so-called tarpaulin produced by placing a reinforcing material between two layers of paper or film, a base cloth is sometimes used as the reinforcing material.
The so far known base cloths for reinforcement include for example the following: Woven fabric of reinforcing fibers; products comprising a warp impregnated with small amounts of an adhesive to prevent fraying and a weft which is a thermally weldable fiber, both yarns being adhered to each other at the intersections thereof; products obtained by adhering a warp to a weft impregnated with an adhesive; and the like.
The base cloth for reinforcement having a form of woven fabric of reinforcing fiber has defects. For example, the warps are flexed above and below wefts at weaving points, so that a force parallel to the face of the fabric is sustained at angled warps. Further, woven fabric is restricted in densities of warp and weft. Production of a woven fabric having a density larger than a specific density is difficult, because the volume of the fiber is restricted by the weaving of warp and weft, and the fabric is liable to be napped by mutual abrasion of warps. Furthermore, as carbon fibers, aromatic polyamide fibers and the like are liable to slip, the production of the fabric having a lower density than a specific density is difficult. Therefore, for keeping a giving interval of the warp, other fiber warp is necessary to be woven into the interval, which lowers the density of the carbon fibers or aromatic polyamide fibers in the woven fabric.
In the method to impregnate the warp with adhesives, penetration of matrix resin into base cloth is disturbed by the influence of the impregnating adhesive to cause a poor reinforcement strength. Also, since thermally weldable fibers are used as a weft, strength in the widthwise direction can hardly be expected.
The method to impregnate the weft with adhesives is much superior in improving the defects of the foregoing method. But, because of the weft being impregnated with adhesives, adhesion of the weft to matrix resins is poor and the reinforcement in the weft direction is not sufficient.